1. Field
The subject technology generally relates to wireless communication, and more specifically to a method and apparatus for enhanced modulation detection.
2. Background
Wireless communication systems are widely deployed to provide various communication services such as voice and data communication. These wireless systems may be multiple-access systems capable of communicating with multiple wireless devices (e.g., cellular phones) to provide communication services to multiple users. Wireless communication systems may employ various wireless communication technologies including Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Divisional Multiple Access (FDMA), Orthogonal FDMA (OFDMA), and others. A widely employed example of TDMA is Global System for Mobile communication (GSM).
A base station in a wireless communication system may transmit data to a mobile station using different modulation schemes, for example, depending on the quality of a radio link between the base station and the mobile station. An example of a communication technology supporting multiple modulation schemes is Enhanced Data rates for GSM Evolution (EDGE), which provides enhanced data rates for GSM networks. An EDGE-enabled base station is capable of transmitting data to a mobile station using either 8-Phase Shift Keying (8-PSK) modulation or Gaussian Minimum Shift Keying (GMSK) modulation. 8-PSK modulation is capable of providing much higher data rates than GMSK modulation. However, GMSK modulation is able to operate in lower Signal-to-Noise (SNR) environments, for example, when the mobile station is located far from the base station.
A base station supporting multiple modulation schemes may use adaptive modulation to determine which modulation scheme to use, for example, based on feedback from the mobile station indicating the radio link quality between the base station and the mobile station. The base station may also adaptively change the coding rate for data transmission based on the feedback from the mobile station.
To properly decode data from a base station, the mobile station needs to demodulate the corresponding received signal based on the modulation scheme used at the base station. However, a mobile station may not know the modulation scheme in advance, for example, when the base station changes the modulation scheme quickly. In this case, the mobile station may detect the modulation scheme from the received signal and demodulate the received signal based on the detected modulation scheme. However, an incorrect detection of the modulation scheme causes the mobile station to demodulate the received signal based on the wrong modulation scheme, leading to failure in the data decoding. For example, the base station may transmit data in blocks, where each block includes a plurality of bursts. In this example, if the mobile station incorrectly detects the modulation scheme for one of the bursts in the block, then the mobile station will likely be unable to properly decode the block.
Accordingly, there is a need for systems and method for enhanced modulation detection.